In an orthogonal frequency division multiplexing (OFDM) system, the orthogonal frequency division multiplexing divides a data stream into several sub-data streams, with each sub-data stream having a relatively low bit rate, and the orthogonal frequency division multiplexing modulates each sub-data stream onto a corresponding subcarrier respectively to send them in parallel, wherein each OFDM subcarrier is not only orthogonal to each other but also has a ½ overlapping.
In a long term evolution (LTE) system, it needs to sufficiently take the peak average power ratio (PAPR) problem of the user terminals (UT) into account, i.e. the instantaneous value of the output signal of the transmitter will have relatively large fluctuation, which will require some components (such as power amplifier, Add/Drop (A/D) converter, Digital-to-Analog (D/A) converter, etc.) in the system to have very large linear dynamic range. And the nonlinearity of these components will also cause the signal with relatively large dynamic range to generate nonlinear distortion. The generated harmonic waves will cause the sub-channels to interfere each other, thus affecting the performance of the OFDM system.
In the LTE system, due to the problem of PAPR, the multi-access mode of sending uplink information uses SC-FDMA. It is because the information symbol of the single carrier system is directly modulated onto the time domain (or some simple deformations), so its PAPR is relatively low. However in a multicarrier system, because there are a plurality of carriers transmitting information symbols simultaneously, and the information symbols carried by each carrier are independent from each other, the PAPR of the multicarrier system is larger than the PAPR of the single carrier system by 2 to 3 dB. High PAPR increases the requirements for power amplification linearly; however, this is very disadvantageous for the UT. Therefore, the best choice of uplink multi-access is a single carrier system with a cycle prefix, i.e. SC-FDMA.
Currently, the research of multi-access based on the OFDM system is a hot spot. But, there is very little research regarding the multi-access mode with a plurality of working frequency points. Taking an LTE system for example, its downlink uses OFDMA, its uplink uses SC-FDMA, and there is only one working frequency point in the system. However, this solution cannot be well suitable for a system which has a plurality of working frequency points (such as LTE-Advanced system and IMT-Advanced system). Therefore, currently it urgently needs a technical solution for multi-access mode when there are a plurality of working frequency points in the system.